The use of electronics is becoming increasingly prevalent in the field of automobiles in recent years, and the wiring used to connect various types of electronic devices installed in vehicles is increasing in both quantity and complexity. Although automotive wires referred to as wire harnesses are used to connect these electronic devices, accompanying the growing prevalence of electronics in vehicles as mentioned above, these wire harnesses are becoming increasingly large.
On the other hand, together with the growing worldwide interest in environmental issues, automobiles are also being required to reduce emission levels of carbon dioxide as well as be lighter in order to improve fuel consumption.
In vehicles such as hybrid vehicles and electric cars in which the use of electronics has increased, there are cases in which wire harnesses can weigh more than about 30 kg. Accordingly, in order to reduce vehicle weight, it is considered to be effective to reduce the weight of wire harnesses, and particularly the weight of automotive wire that accounts for a large proportion of the weight of those wire harnesses.
One method that has been considered for reducing the weight of automotive wire consists of the use of materials having a lower specific gravity for the materials serving as lead wires used in automotive wires.
Examples of methods for using materials having a low specific gravity include a method that uses aluminum for the lead conductors composing automotive wires, and a method that uses Cu-coated Al wires in which a core composed of aluminum is coated with copper (see, for example, Patent Document 1 and Patent Document 2). In addition, automotive wire is also known that uses a Cu alloy and the like for the lead conductor (see, for example, Patent Document 3).
However, there are also cases in which automotive wire is required to be lightweight while at the same time having high strength, such as breaking strength in excess of 1000 MPa.
In the case of using a lightweight material as described above, for example, aluminum wires were unable to be used as automotive wire due to the low strength and in terms of contact resistance with terminals. In addition, Cu-coated Al wire and Cu alloy were also unable to be used in consideration of strength. Moreover, when the cross-sectional area of the lead wire is increased in order to secure strength, this leads to increased weight and size of the wire harness. Consequently, it is necessary to achieve both a narrow diameter and high strength while realizing reduced weight for use as automotive wire.
An example of a method for realizing an automotive wire having both a narrow diameter and high strength consists of using wire obtained by plating Cu onto high-strength stainless steel wire (see, for example, Patent Document 4). This automotive wire secures strength by employing stainless steel wire as a tension member, and is formed by forming Cu as an electrically conductive layer around the stainless steel wire using plating method. As a result of employing this configuration for an automotive wire, both light weight and high strength required by recent automotive wires are realized.